• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.6
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• pp.1-5
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• 2008

As bare Fiber Bragg Grating (FBG) sensors are very fragile, bare FBG without encapsulation is not properly applied in practical infrastructures directly due to the harsh environment in practical engineering. Steel sleeve packaged FBG strain sensor is widely used in civil engineering. Since FBG senses both strain and temperature simultaneously, for accurate measurement of strain, temperature compensation for FBG strain sensors is indispensable. In this paper, based on the FBG's strain and temperature sensing principles, the temperature compensation techniques for steel sleeve packaged FBG sensors are brought forward. And the experiment of concrete early-age shrinkage monitoring by dual FBG sensors is carried out to test the feasibility of the temperature compensation technique.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.89-90
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• 2009

FBG temperature sensor and strain sensor has been used to monitoring shrinkage and temperature of concrete retaining wall in construction site in its casting early age. The test results indicate that this monitoring method is a practical method for monitoring concrete at very early age. The monitoring technique used in this research could be extended to monitor shrinkage and temperature for mass concrete structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.137-144
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• 2019

In coupon test of carbon fiber reinforced polymers (CFRP) as brittle materials, the converted strain derived from total deformation and effective length was introduced and its advantages were described. In general, measured value from strain gauge is used for determining the tensile properties of material, but it is not quite effective in CFRP because brittle material can not redistribute its stress and it only represents local behavior. For this reason, the converted strain response can be utilized effectively as a supplementary indicator, which evaluated the average value of tensile properties in brittle material and confirmed the strain measured by strain gauge. In addition, the converted strain clearly visualized 1) the effect of initial internal strain caused by fabrication errors and setup misalignment when applying gripping force and 2) post-response of partial rupture of CFRP caused by non-uniform strain distribution. non-uniform strain distribution.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.06b
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• pp.51-64
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• 1999

가스터빈에 사용되는 소재는 여타 금속소재에 비하여 고온 기계적 특성은 우수한 반면 상대적으로 단조성이 떨어지기 때문에, 금속소재의 단조성에 대한 이해와 단조 공정별 장단점을 파악하여 단조공정 설계에 반영하여야 한다. 가스터빈용 Ni합금의 경우 고온기계적 성질은 결정립 크기에 크게 의존한다. 결정립 크기는 기계적 성질에 직접적으로 영향을 미치는데, 동적재결정의 경우 초기 결정립크기, 변형률, 변형속도, 온도 뿐만 아니라 결정립계에 석출된 제2상에 의해서 크게 영향을 받기 때문에 이들 상의 고용온도를 파악하여 단조공정 설계에 반영하여야 한다. 유한요소법으로 변형률과 온도분포를 해석함으로써 단조품 내의 결정립 분포를 효과적으로 예측할 수 있다. 다단계 단조 경우, 최종 단조품의 결정립 크기는 단계별 단조 온도 및 변형률 배분 등에 따라 변하므로 이를 고려하여야 한다.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.2
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• pp.80-91
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• 1999

This paper presents the stress-strain , volumetric strain characteristics of the Pocheon weathered residual granite soil with variation of the initial water content under drained conditions. A series of consolidated drained triaxial compressiion tests and isotrpc compression tests with various initial water content on specimens were performed. All material parameters of Lade's double work hardening model were determined by using the results of tests. Most aspects of the soil behavior measured in the triaxial compression tests were reproduced with good accuracy by the constitutive model . Therefore double work hardening model has been shown to be applicable to weathered residual granite soil.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.105-106
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• 2010

FBG temperature sensor and strain sensor has been used to monitoring shrinkage and temperature of concrete cable-stayed girder bridge site in its casting early age, The monitoring method using this study is expected to used a practical method.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.3
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• pp.159-168
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• 2012

본 연구에서는 해성 점성토에 대하여 반복 삼축시험을 실시하고 응력-변형률 관계 및 유효응력경로 특성 분석을 통해 동적 변형 및 강도 특성을 조사하였다. 시험에 사용된 시료는 일본 도쿠시마현의 코마츠시마 항 인근에서 채취된 점성토이며, 반복 삼축시험으로 동적 비배수 삼축시험, 동적 비배수 삼축시험 후 동적 삼축변형시험, 다단계 동적 비배수 삼축시험, 동적 삼축 변형시험 등 4종류의 시험을 수행하고, 시험 주파수로서 0.1 및 0.01 Hz을 적용하였다. 본 연구 결과 0.01 Hz로 수행된 동적 삼축시험 결과는 0.1 Hz로 수행된 삼축시험 결과보다 평균유효응력의 감소량이 크며, 반복 하중은 해성 점성토의 구조적 약화를 초래하고 초기 거동시 발생하는 간극수압과 밀접하게 관련이 있는 것으로 나타났다. 또한 미소변형률 영역에서 등가 탄성계수는 시험 횟수가 증가함에 따라 점차 감소하며, 감쇠비는 점차 증가하는 것으로 보아 변형계수는 반복 하중으로 인한 전단변형률의 축척에 따른 변형률 의존 거동에 관련하는 것으로 판단된다.

• Geotechnical Engineering
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• v.13 no.4
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• pp.109-120
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• 1997

In the working stress conditions, the strain level in a soil mass experienced by existing structures and during construction is less than about 0.1-1%. In order to analyse the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at small strains, needs to be developed. The purpose of this paper is to measure the small-strain shear modulus of soils by using pressuremeter test(PMT). PMT is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. For the accurate small strain measurements without initial disturbance effect, the unloading-reloading cycle was used and the measured modulus was corrected in view of the relevant stress and strain levels around the PMT probe during testing. Not only in the calibration chamber but in the field, PMT tests were performed on the cohesionless soils. The variation in shear modulus with strain amplitude ranging from 10-2% to 0.5% was reliably determined by PMT PMT results were also compared with other in-situ and laboratory test results. Moduli obtained from different testing techniques matched very well if the effect of strain amplitude was considered in the com pall son.

• Elastomers and Composites
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• v.42 no.3
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• pp.168-176
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• 2007

When the rubber vulcanizates reinforced with carbon black or silica are subjected to cyclic loading from its virgin state, the stress required on reloading is less than that on the initial loading. This stress softening phenomenon is referred to as the Mullins effect. The strain energy function of rubber vulcanizates was investigated using theory of pseudo-elasticity incorporated damage parameter that Ogden and Roxburgh have proposed to describe the damage-induced stress softening effect in rubber-like solids. The quasi-static cyclic loading test was performed using the NR-SBR vulcanizates reinforced with carbon black, and then the effect of a damage parameter to stress-strain curve in reloading and subsequent reloading paths was studied. The strain energy function of the rubber vulcanizates with a different filler content was also evaluated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.10a
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• pp.191-196
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• 1993

본 연구에서는 이러한 방진궤도의 성능을 파악하고 또 적절한 방진궤도의 설계를 위하여 먼저 모형화하는 방법을 제시하였다. 이를 위해서는 궤도를 구성하는 방진요소의 특성을 결정하는 것이 필수적이므로 현재 사용되고 있 는 점탄성 방진재에 대하여 주파수, 온도, 초기 변형률, 동적변형률등 여러가 지 인자에 대한 물성치를 구하였으며, 이를 이용하여 궤도계의 진동전달 특 성을 파악하고 고찰하였다.